Processed slag and methods for producing same

ABSTRACT

Hydrometallurgical systems, methods, and compositions are described in which organic amine-based lixiviants are utilized in the selective removal of carbonate-forming alkaline earth elements from slag. The resulting processed slag has a reduced tendency to form carbonate salts on environmental exposure, and reduced tendency to fracture due to the formation of such salts. The lixiviant used can be regenerated and recycled for use in subsequent iterations of the process.

This application is a divisional application of U.S. patent applicationSer. No. 15/638,103, filed Jun. 29, 2017, which is a continuation inpart of U.S. patent application Ser. No. 14/073,503, filed Nov. 6, 2013,which claims priority to U.S. Provisional Application No. 61/796,371,filed Nov. 7, 2012; U.S. Provisional Application No. 61/797,354, filedDec. 4, 2012; and U.S. Provisional Application No. 61/855,443, filed May14, 2013. These and all other referenced extrinsic materials areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The field of the invention is hydrometallurgy, particularly as it isrelated to the removal or recovery of alkaline earth elements.

BACKGROUND

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

Slag is a byproduct of metal (for example, iron or steel) recovery fromores, and includes a broad range of non-desired metal oxides and saltsin addition to non-metallic components. The vast majority of slags areferrous slags produced by the iron/steel industry, with approximately12% of slag resulting from processing of ores to recovery non-ferrousmetals such as copper and zinc.

Although considered to be waste material, various uses have been foundfor slags produced by ore refining processes. For example, when cooledslowly ferrous slags form a vesicular rock-like material (air-cooledblast furnace slag) that can be utilized as load-bearing fills and roadbases. Such material can, after crushing and grading, also be utilizedas concrete aggregate and/or sand, as a filter medium, or as a componentof fiber insulation. If processed using high volume water sprays, suchferrous slags yield a glassy product that is similar to beach sand.Slags processed in this fashion can be used as a partial replacement forPortland cement in concrete, reinforcement of embankments, and for minebackfilling. Some slags are generated by the injection of oxygen into amixture of molten iron, metal scrap, and flux (typically lime) toprovide basic oxygen furnace slag. This cools to form a dense rock-likematerial that can be blended with other materials to form pavements,used as an aggregate in skid-resistant asphalt, concrete aggregate, andconstruction fill.

Such slags, however, can include significant amounts of calcium,magnesium, and other elements in the form of hydroxides, oxides, and/orsalts that are reactive with water and/or atmospheric carbon dioxide.The resulting formation of carbonate and/or bicarbonate salts can resultin fracturing or fragmentation of the slag. This fragmentation, in turn,reduces the utility of the slag in structural materials (such asconcrete) and applications (such as fills).

Hydrometallurgy has been used to isolate metals from a variety ofminerals, ores, and other sources. Typically, ore is crushed andpulverized to increase the surface area prior to exposure to thesolution (also known as a lixiviant). Suitable lixiviants solubilize thedesired metal, and leave behind undesirable contaminants. Followingcollection of the lixiviant, the metal can be recovered from thesolution by various means, such as by electrodeposition or byprecipitation from the solution.

Previously known methods of hydrometallurgy have several problems.Identification of lixiviants that provide efficient and selectiveremoval of the desired metal or metals has been a significant technicalbarrier to their adoption in the isolation of some metals. Similarly,the expense of lixiviant components, and difficulties in adapting suchtechniques to current production plants, has limited their use.

Approaches have been devised to address these issues. United StatesPatent Application No. 2004/0228783 (to Harris, Lakshmanan, and Sridhar)describes the use of magnesium salts (in addition to hydrochloric acid)as a component of a highly acidic lixiviant used for recovery of othermetals from their oxides, with recovery of magnesium oxide from thespent lixiviant by treatment with peroxide. All publications identifiedherein are incorporated by reference to the same extent as if eachindividual publication or patent application were specifically andindividually indicated to be incorporated by reference. Where adefinition or use of a term in an incorporated reference is inconsistentor contrary to the definition of that term provided herein, thedefinition of that term provided herein applies and the definition ofthat term in the reference does not apply. Such highly acidic andoxidative conditions, however, present numerous production and potentialenvironmental hazards that limit their utility. In an approach disclosedin U.S. Pat. No. 5,939,034 (to Virnig and Michael), metals aresolubilized in an ammoniacal thiosulfate solution and removed into animmiscible organic phase containing guanidyl or quaternary aminecompounds. Metals are then recovered from the organic phase byelectroplating.

A similar approach is disclosed in U.S. Pat. No. 6,951,960 (to Perraud)in which metals are removed from an aqueous phase into an organic phasethat contains an amine chloride. The organic phase is then contactedwith a chloride-free aqueous phase that removes metal chlorides from theorganic phase. Amines are then regenerated in the organic phase byexposure to aqueous hydrochloric acid. Application to alkaline earthelements (for example, calcium) is not clear, however, and the disclosedmethods necessarily involve the use of expensive and potentially toxicorganic solvents.

In a related approach, European Patent Application No. EP1309392 (toKocherginsky and Grischenko) discloses a membrane-based method in whichcopper is initially complexed with ammonia or organic amines. Thecopper:ammonia complexes are captured in an organic phase containedwithin the pores of a porous membrane, and the copper is transferred toan removing agent held on the opposing side of the membrane. Such anapproach, however, requires the use of complex equipment, and processingcapacity is necessarily limited by the available surface area of themembrane.

Methods for capturing CO₂ could be used to recover alkaline earthmetals, but to date no one has appreciated that such could be done.Kodama et al. (Energy 33(2008), 776-784) discloses a method for CO₂capture using a calcium silicate (2CaO.SiO₂) in association withammonium chloride (NH₄Cl). This reaction forms soluble calcium chloride(CaCl₂), which is reacted with carbon dioxide (CO₂) under alkalineconditions to form insoluble calcium carbonate (CaCO₃) and releasechloride ions (Cl—).

Kodama et al. uses clean forms of calcium to capture CO₂, but is silentin regard to the use of other alkaline earth elements in this chemistry.That makes sense from Kodoma et al.'s disclosure, which notes that ahigh percentage (approximately 20%) of the NH₄Cl used is lost in thedisclosed process, requiring the use of additional equipment to captureammonia vapor. This loss results in significant process inefficiencies,and raises environmental concerns. Japanese Patent Application No.2005097072 (to Katsunori and Tateaki) discloses a similar method for CO₂capture, in which ammonium chloride (NH₄Cl) is dissociated into ammoniagas (NH₃) and hydrochloric acid (HCl), the HCl being utilized togenerate calcium chloride (CaCl₂) that is mixed with ammonium hydroxide(NH₄OH) for CO₂ capture.

International Application WO 2012/055750 (to Tavakkoli et al) disclosesa method for purifying calcium carbonate (CaCO₃), in which impure CaCO₃is converted to impure calcium oxide (CaO) by calcination. The resultingCaO is treated with ammonium chloride (NH₄Cl) to produce calciumchloride (CaCl₂), which is subsequently reacted with high purity carbondioxide (CO₂) to produce CaCO₃ and NH₄Cl, with CaCO₃ being removed fromthe solution by crystallization with the aid of seed crystals. Withoutmeans for capturing or containing the ammonia gas that would result fromsuch a process, however, it is not clear if the disclosed method can beadapted to an industrial scale.

Thus, there is still a need for a scalable and economical method toreduce the reactivity of slags with water and/or carbon dioxide.

SUMMARY OF THE INVENTION

Inventors have found that removal of carbonate-forming alkaline earthmetals from slags produced by industrial processes provides a processedslag with a reduced tendency to form carbonate salts, which in turnprovides improved mechanical stability and resistance to fragmentation.Alkaline earth elements are removed selectively using a lixiviant, whichcan be subsequently regenerated and recycled through the process.

One embodiment of the inventive concept is a method for producing aprocessed slag, which includes the steps of contacting a slag rawmaterial with a lixiviant (which can include an organic amine cationcontaining carbon and a counterion), forming the processed slag and asupernatant that includes an uncharged organic amine and a solublecomplex of the cation of the alkaline earth element and the counterion.The resulting processed slag is separated from the supernatant, and hasa reduced content of the first alkaline earth element relative to theslag. The lixiviant can be regenerated by regenerating the organic aminecation through addition of a precipitant (e.g. carbon dioxide and/orcarbonic acid) to the first supernatant, which can also result inprecipitation of the alkaline earth element. This regenerated organicamine cation can be subsequently used to treat the slag. In someembodiments pH during regeneration of the organic amine cation is lessthan about 7, or between 6 and 7. In some embodiments the organic aminehas a pKa between 8 and 14. The lixiviant can be formed by adding anacid to the uncharged organic amine in the presence of the slag.

In some embodiments the slag can also include an additional alkalineearth element. In such embodiments the processed slag can be furthercontacted with a second lixiviant that includes a second organic aminecation and a second counterion. This results in the formation of asecond processed slag and a second supernatant that includes anuncharged second organic amine and a complex of the additional alkalineearth cation and the second counterion. In such embodiments the secondprocessed slag has a reduced content of this additional alkaline earthelement relative to the slag and/or to the processed slag. The secondprocessed slag is separated from the second supernatant, which can inturn be treated with a second precipitant to regenerate the secondorganic cation. In some embodiments this second precipitant can be thesame species as the precipitant utilized in the initial treatment of theslag.

In an alternative method for producing a processed slag, a slag thatincludes a first alkaline earth element and a second alkaline earthelement is contacted with a lixiviant that includes a first organicamine cation, a second organic amine cation, and a counterion. Thisresults in the generation of a processed slag and a first supernatant.The first supernatant includes an uncharged first organic amine, anuncharged second organic amine, a first complex comprising a firstalkaline earth metal cation and the counterion, and a second complexcomprising a second alkaline earth metal cation and the counterion. Theresulting processed slag has a reduced content of the first alkalineearth element and the second alkaline earth element relative to theslag, and is separated from the first supernatant. The first alkalineearth metal cation is removed from the first supernatant (for example,by the addition of a precipitant) to form a second supernatant, fromwhich the second alkaline earth metal cation is subsequently removed(for example, by the addition of a precipitant). Examples of suitableprecipitants include carbon dioxide and carbonic acid. In this processthe first organic amine cation and/or the second organic amine cationare regenerated in the second supernatant. In some embodiments the firstorganic amine cation and the second organic amine cation are the samespecies; in other embodiments the first organic amine cation and thesecond organic amine cation are different species.

Another embodiment of the inventive concept is processed slag producedby selective removal of an alkaline earth element from a slag. Such aprocessed slag can have less than 60%, less than 40%, and/or less than20% of the first alkaline earth element content of the slag. Theprocessed slag is characterized by having a reduced carbonate contentrelative to that of the slag following environmental exposure.Similarly, the processed slag is characterized by having improvedresistance to compressive stress or lateral stress relative to that ofthe slag following environmental exposure.

Another embodiment of the inventive concept is a construction materialthat includes a processed slag produced by selective removal of a firstalkaline earth element from a slag. Such a processed slag can have lessthan 60%, less than 40%, and/or less than 20% of the first alkalineearth element content of the slag. Examples of such constructionmaterials include concrete, concrete sand, concrete aggregate, andasphalt aggregate. Other examples of such construction materials includeroad bed material, railroad track bed material, and fill material.

Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the following detaileddescription of preferred embodiments, along with the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts steps A through F of an example of a methodof the inventive concept in which calcium is removed from slag togenerate a processed slag, using an organic amine chloride lixiviantthat is regenerated.

FIG. 2 schematically depicts a method of the inventive concept, in whichan alkaline earth element is removed from slag using a lixiviant toproduce a processed slag. The lixiviant is subsequently regenerated.

FIG. 3 schematically depicts another method of the inventive concept, inwhich different alkaline earth elements are removed from slag in astepwise fashion to produce a processed slag.

FIG. 4 schematically depicts an alternative embodiment of the inventiveconcept, in which different alkaline earth elements are removed fromslag to produce a processed slag.

FIG. 5 illustrates the composition of a steel slag.

FIG. 6 schematically depicts processing of a steel slag by a method ofthe inventive concept.

FIG. 7A-C show the results of systems, methods, and compositions of theinventive concept. FIG. 7A shows pH changes over time as an alkalineearth element is removed from a low grade source using an organic aminelixiviant. FIG. 7B shows pH changes over time as an alkaline earthelement is removed from a low grade source using a different organicamine lixiviant. FIG. 7C shows pH changes over time as an removedalkaline earth element is recovered through the use of a precipitant.FIG. 7C is a photomicrograph of a precipitated calcium carbonate productof systems, methods, and compositions of the inventive concept.

DETAILED DESCRIPTION

Throughout the following discussion, numerous references will be maderegarding lixiviants. A lixiviant should be understood to be a chemicalentity that has the ability to selectively remove metals or metal ionsfrom inorganic or organic solids in an aqueous or other solvent mixture.

The inventive subject matter provides apparatus, systems and methodswhich provide a processed slag with a reduced tendency to fragment. Thisis achieved by selective removal of metals (e.g. calcium and/ormagnesium) that form carbonates on exposure to water and carbon dioxide.Such removal can be essentially complete (i.e. >90% removal) or partial(i.e. greater than 20%, 25%, 30%, 35%, 40%, 45%, or 50% removal),depending on the composition of the slag and/or duration of treatment.Such processed slags are particularly useful in structural and fillmaterials as the reduced carbonate content reduces fragmentation andsubsequent mechanical destabilization of the particles of processedslag.

Processed slags are generated by subjecting ferrous and/or non-ferrousslag to lixiviant-based processes that selectively remove metals, metaloxides, and/or metal salts that react with components of the environment(such as water and/or carbon dioxide) to for salts that promotefragmentation. The slag is contacted with a lixiviant that selectivelysolubilizes problematic metallic elements (e.g. calcium and/ormagnesium) from the slag, leaving the processed slag as an insolublematerial that is readily separated from an aqueous supernatant. Slag canbe milled, pulverized, graded, or otherwise re-sized prior to contactwith the lixiviant in order to improve reaction kinetics and provide aprocessed slag having a desired size and/or shape. The lixiviant used insuch processes can be regenerated from the soluble, aqueous fraction sogenerated and re-used, and in some embodiments can be used in smallamounts relative to the amount of carbonate-forming metallic element(e.g. calcium and/or magnesium) present in the slag.

The following discussion provides many exemplary embodiments of theinventive subject matter. Although each embodiment represents a singlecombination of inventive elements, the inventive subject matter isconsidered to include all possible combinations of the disclosedelements. Thus if one embodiment comprises elements A, B, and C, and asecond embodiment comprises elements B and D, then the inventive subjectmatter is also considered to include other remaining combinations of A,B, C, or D, even if not explicitly disclosed.

In some embodiments, the numbers expressing quantities of ingredients,properties such as concentration, reaction conditions, and so forth,used to describe and claim certain embodiments of the invention are tobe understood as being modified in some instances by the term “about.”Accordingly, in some embodiments, the numerical parameters set forth inthe written description and attached claims are approximations that canvary depending upon the desired properties sought to be obtained by aparticular embodiment. In some embodiments, the numerical parametersshould be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof some embodiments of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspracticable. The numerical values presented in some embodiments of theinvention may contain certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.

Unless the context dictates the contrary, all ranges set forth hereinshould be interpreted as being inclusive of their endpoints andopen-ended ranges should be interpreted to include only commerciallypractical values. Similarly, all lists of values should be considered asinclusive of intermediate values unless the context indicates thecontrary.

As used in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

The recitation of ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value with a range is incorporated into the specification asif it were individually recited herein. All methods described herein canbe performed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g. “such as”) provided with respectto certain embodiments herein is intended merely to better illuminatethe invention and does not pose a limitation on the scope of theinvention otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element essential to thepractice of the invention.

Groupings of alternative elements or embodiments of the inventiondisclosed herein are not to be construed as limitations. Each groupmember can be referred to and claimed individually or in any combinationwith other members of the group or other elements found herein. One ormore members of a group can be included in, or deleted from, a group forreasons of convenience and/or patentability. When any such inclusion ordeletion occurs, the specification is herein deemed to contain the groupas modified thus fulfilling the written description of all Markushgroups used in the appended claims.

The inventors have discovered a hydrometallurgical method for theselective removal of alkaline earth elements (i.e., alkaline earthmetals), such as members of the alkaline earth family (e.g. calciumand/or magnesium) from slag materials produced by metal ore refiningprocesses, through the use of lixiviants that include organic amines. Inaddition the inventors have determined that such organic amine-basedlixiviants can be regenerated using carbon dioxide.

Embodiments of the inventive process can include at least one compoundof the general composition depicted in Compound 1 for use with a slag orother material that contains one or more a form(s) of an alkaline earth(AE) hydroxide forming species, that can be hydrated to form AE(OH)x orother hydrated species that would react with lixiviants of the formfound in Equation 1. Alternatively, alkaline earth elements can bepresented as oxides, for example calcium oxide (CaO), that can formhydroxides on reaction with water. Such hydrated forms may be present inthe material as it is obtained from nature or can be introduced byprocessing (for example through treatment with a base, hydration, or byoxidation), and can be stable or transient. Selective removal of thedesired alkaline earth can be based on the presence of a metal hydroxidethat has a stronger basicity than the organic amine-based lixiviantsused in the removal process.

Organic amines of the inventive concept have the general formula shownin Compound 1, where N is nitrogen, H is hydrogen, and X is a counterion(i.e., a counter anion).

Ny,R₁,R₂,R₃,H—Xz   Compound 1

Suitable counterions can be any form or combination of atoms ormolecules that produce the effect of a negative charge. Counterions canbe halides (for example fluoride, chloride, bromide, and iodide), anionsderived from mineral acids (for example nitrate, phosphate, bisulfate,sulfate, silicates), anions derived from organic acids (for examplecarboxylate, citrate, malate, acetate, thioacetate, propionate and,lactate), organic molecules or biomolecules (for example acidic proteinsor peptides, amino acids, nucleic acids, and fatty acids), and others(for example zwitterions and basic synthetic polymers). For example,monoethanolamine hydrochloride (MEA.HCl, HOC₂H₄NH₃Cl) conforms toCompound 1 as follows: one nitrogen atom (N₁) is bound to one carbonatom (R₁═C₂H₅O) and 3 hydrogen atoms (R₂, R₃ and H), and there is onechloride counteranion (X₁═Cl—). Compounds having the general formulashown in Compound 1 can have a wide range of acidities, and an organicamine of the inventive concept can be selected on the basis of itsacidity so that it can selectively react with one or more alkaline earthmetal salts or oxides from a sample containing a mixture of alkalineearth metal salts or oxides. Such a compound, when dissolved in water oranother suitable solvent, can (for example) effectively remove thealkaline earth element calcium presented in the form calcium hydroxidein a suitable sample (e.g. steel slag). Equation 1 depicts a primarychemical reaction in removing an insoluble alkaline earth (AE) salt (inthis instance a hydroxide salt) from a matrix using an organic aminecation (OA-H+)/counterion (Cl—) complex (OA-H+/Cl—) as a lixiviant. Notethat the OA-H+/Cl— complex dissociates in water into OA-H+ and Cl—.

AE(OH)₂(solid)+2OA-H+(aq)+2Cl-(aq)→AECl₂(aq)+2OA(aq)+2H₂O   Equation 1

The counterion (Cl—) is transferred from the organic amine cation(OA-H+) to the alkaline earth salt to form a soluble alkalineearth/counterion complex (AECl₂), uncharged organic amine (OA), andwater. Once solubilized the alkaline earth/counterion complex can berecovered from solution by any suitable means. For example, addition ofa second counterion (SC) in an acid form (for example. H₂SC), whichreacts with the alkaline earth cation/counterion complex to form aninsoluble alkaline earth salt (AESC), can be used to precipitate theremoved alkaline earth from supernatant and release the counterion toregenerate the organic amine cation/counterion pair, as shown inEquation 2.

AECl₂(aq)+2OA(aq)+H₂SC→AESC salt(solid)+2OA+(aq)+2Cl—   Equation 2

Examples of suitable second counterions include polyvalent cations, forexample carbonate (which can be supplied as CO₂), sulfate, sulfite,chromate, chlorite, and hydrogen phosphate.

Alternatively, pH changes, temperature changes, or evaporation can beused to precipitate the solubilized alkaline earth. In some embodiments,the alkaline earth element can be recovered by electrodepositionprocesses, such as electrowinning or electrorefining. In otherembodiments of the inventive concept the solubilized alkaline earthelement can be recovered by ion exchange, for example using a fixed bedreactor or a fluidized bed reactor with appropriate media.

In a preferred embodiment of the inventive concept, the alkaline earthelement can be recovered by precipitation through reaction of themixture with carbon dioxide (CO₂), which advantageously regenerates thelixiviant as shown below. It should be appreciated that the process ofrecovering the alkaline earth element can be selective, and that suchselectivity can be utilized in the recovery of multiple alkaline earthelements from a single source as described below.

The organic amine cation/counterion complex can be produced from theuncharged organic amine to regenerate the 0A-H+/Cl— lixiviant, forexample using an acid form of the counterion (H—Cl), as shown inEquation 3.

OA(aq)+H—Cl(aq)→OA-H+(aq)+Cl—   Equation 3

In some embodiments of the inventive concept the reaction described inEquation 3 can be performed after the introduction of an unchargedorganic amine to a source of an alkaline earth element, with thelixiviant being generated afterwards by the addition of an acid form ofthe counterion. This advantageously permits thorough mixing of thealkaline earth source with a lixiviant precursor prior to initiating thereaction.

Organic amines suitable for the removal of alkaline earth elements (forexample from calcium containing or, steel slag, and other materials) canhave a pKa of about 7 or about 8 to about 14, and can include protonatedammonium salts (i.e., not quaternary). Examples of suitable organicamines for use in lixiviants include weak bases such as ammonia,nitrogen containing organic compounds (for example monoethanolamine,diethanolamine, triethanolamine, morpholine, ethylene diamine,diethylenetriamine, triethylenetetramine, methylamine, ethylamine,propylamine, dipropylamines, butylamines, diaminopropane, triethylamine,dimethylamine, and trimethylamine), low molecular weight biologicalmolecules (for example glucosamine, amino sugars,tetraethylenepentamine, amino acids, polyethyleneimine, spermidine,spermine, putrescine, cadaverine, hexamethylenediamine,tetraethylmethylenediamine, polyethyleneamine, cathine, isopropylamine,and a cationic lipid), biomolecule polymers (for example chitosan,polylysine, polyornithine, polyarginine, a cationic protein or peptide),and others (for example a dendritic polyamine, a polycationic polymericor oligomeric material, and a cationic lipid-like material), orcombinations of these. In some embodiments of the inventive concept theorganic amine can be monoethanolamine, diethanolamine, ortriethanolamine, which in cationic form can be paired with nitrate,bromide, chloride or acetate anions. In other embodiments of theinventive concept the organic amine can be lysine or glycine, which incationic form can be paired with chloride or acetate anions. In apreferred embodiment of the inventive concept the organic amine ismonoethanolamine, which in cationic form can be paired with a chlorineanion.

Such organic amines can range in purity from about 50% to about 100%.For example, an organic amine of the inventive concept can have a purityof about 50%, about 55%, about 60%, about 65%, about 70%, about 75%,about 80%, about 85%, about 90%, about 95%, about 97%, about 99%, orabout 100%. In a preferred embodiment of the inventive concept theorganic amine is supplied at a purity of about 90% to about 100%. Itshould be appreciated that organic amines can differ in their ability tointeract with different members of the alkaline earth family and withcontaminating species, and that such selectivity can be utilized in therecovery of multiple alkaline earths as described below.

Inventors further contemplate that zwitterionic species can be used insuitable lixiviants, and that such zwitterionic species can formcation/counterion pairs with two members of the same or of differentmolecular species. Examples include amine containing acids (for exampleamino acids and 3-aminopropanoic acid), chelating agents (for exampleethylenediamine-tatraacetic acid and salts thereof, ethylene glycoltetraacetic acid and salts thereof, diethylene triamine pentaacetic acidand salts thereof, and1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid and saltsthereof), and others (for example betaines, ylides, andpolyaminocarboxylic acids).

Organic amines for use in lixiviants can be selected to have minimalenvironmental impact. The use of biologically derived organic amines,such as glycine, is a sustainable practice and has the beneficial effectof making processes of the inventive concept more environmentally sound.In addition, it should be appreciated that some organic amines, such asmonoethanol-amine, have a very low tendency to volatilize duringprocessing. In some embodiments of the inventive concept an organicamine can be a low volatility organic amine (i.e., having a vaporpressure less than or equal to about 1% that of ammonia under processconditions). In preferred embodiments of the inventive concept theorganic amine is a non-volatile organic amine (i.e., having a vaporpressure less than or equal to about 0.1% that of ammonia under processconditions). Capture and control of such low volatility and non-volatileorganic amines requires relatively little energy and can utilize simpleequipment. This reduces the likelihood of such low volatility andnon-volatile organic amines escaping into the atmosphere andadvantageously reduces the environmental impact of their use.

An example of an application of the inventive concept is in theselective removal of insoluble calcium hydroxide from slag, using anammonium chloride containing lixiviant. Any slag or similar industrialwaste product that contains a basic form of calcium can be suitable foruse in a process of the inventive concept, for example steel slag, ironslag, fly ash, cement kiln dust, ash, shale ash, and acetylene catalystwaste. In preferred embodiments of the inventive concept the slag is abyproduct of the processing of iron/steel ore. Equation 4 represents areaction that takes place on contacting calcium hydroxide(Ca(OH)₂))-containing steel slag with an ammonium chloride lixiviant.

Ca(OH)₂(solid)+2NH₄+(aq)+2Cl-(aq)→CaCl₂(aq)+2NH₃(aq)+2H₂O   Equation 4

Calcium is removed from the slag as soluble calcium chloride (CaCl₂),with the generation of uncharged ammonia (NH₃) and water.

A soluble alkaline earth salt, for example calcium chloride and thesoluble ammonia from Equation 4 (or soluble ammonium ion if the reactionis metal oxide/hydroxide limited) can easily be separated from theinsoluble solid residue, for example by filtration. Once separated, thesoluble aqueous fraction can be used as-is if the target process cantolerate the small quantity of ammonia or ammonium chloride.Alternatively, the solution can be further processed as needed. In apreferred embodiment of the inventive concept the lixiviant isregenerated and the alkaline earth calcium is recovered as an insolublesalt through the addition of carbon dioxide (CO₂), as shown in Equation5. Note that aqueous CO₂ can be in the form of ionized carbonic acid(i.e., 2H+ plus CO₃ ²⁻).

CaCl₂(aq)+2NH₃(aq)+CO₂(aq)+H₂O→CaCO₃(solid)+2NH₃(aq)++2Cl-(aq)  Equation 5

It should be appreciated that systems, methods, and compositions of theinventive concept can also be used to selectively remove and/or remove adesired alkaline earth element (such as calcium) from a slag containingother contaminants, for example other alkaline earth elements. By usingthe lixiviants described herein, one skilled in the art can exploit thevarying degrees of basicity associated with each alkaline earth element,and choose a lixiviant of corresponding acidity to achieve selectiveremoval.

As noted above, in many instances the use of a low volatility and/ornon-volatile lixiviant is desirable. An example of such a process of theinventive concept is the removal of calcium (Ca) from slag using anon-volatile organic amine, such as monoethanolamine hydrochloride, asshown in steps A to F of FIG. 1A. As shown in step A of FIG. 1, a tank100 or other suitable arrangement includes an aqueous solution of anorganic amine 110 (in this instance monoethanolamine) and a slag 120containing calcium hydroxide (Ca(OH)₂ and unwanted contaminants (CONT).In some embodiments the slag 120 can be milled, ground, pulverized,sieved, or otherwise resized prior to contact with the lixiviant. Thesolvent used can be any protic or highly polar solvent that can supportthe solvation of calcium salts in large amounts. Examples of suitablesolvents include water, glycerol, and water glycerol mixtures.

The amount of organic amine can be optimized for efficient alkalineearth removal and minimal use of organic amine. For example, in someembodiments the amount of a monovalent organic amine can be selected tobe at least about twice that of the available alkaline earth element. Inpreferred embodiments of the inventive concept the amount of amonovalent organic amine can be selected to be at least about 2.1 timesto about 2.05 times that of the available alkaline earth element.Amounts of organic amines with greater charges can be adjustedaccordingly (for example, an organic amine that forms a divalent cationcan be used in at least a 1:1 ratio with the available alkaline earthelement). In other embodiments, the amount of lixiviant species utilizedcan be less than that of the amount of alkaline earth to be removed fromthe slag (i.e. present in substoichiometric amounts). In suchembodiments the amount of lixiviant present can be selected to be lessthan about 100%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 15%, 10%,5%, 3%, 1%, 0.5%, or 0.1% of the alkaline earth species present in theslag on a molar basis.

Reaction conditions can additionally be optimized by adjusting thesurface area available for the reaction. Particle size of the calciumcontaining raw material can be reduced prior to exposure to lixiviant,for example by grinding, milling, or sifting. In some embodiments of theinventive concept the particle size can range from about 0.05 mm toabout 1 mm. In other embodiments of the inventive concept the particlesize can range from about 0.05 to about 0.25 mm. In a preferredembodiment the particle size can range from about 0.05 mm to about 0.125mm.

The calcium content of the aqueous solution phase can also be adjustedto provide efficient removal. In some embodiments of the inventiveconcept the Ca content is controlled such that the mass ratio of Ca (interms of CaO to water) can range from about 0.02 to about 0.5. In otherembodiments the mass ratio of Ca can range from about 0.05 to about0.25. In a preferred embodiment of the inventive process the mass ratioof Ca can range from about 0.1 to about 0.15.

The removal process can be initiated as shown in step B of FIG. 1 by theaddition of an acid form of a counterion 130, in this instancehydrochloric acid (HCl), which generates an organic acidcation/counterion pair 140 (in this instance monoethanolaminehydrochloride (MEA+/Cl—)) to form a lixiviant solution. Monoethanolaminehydrochloride (MEA.HCl, HOC₂H₄NH₃Cl) conforms to Compound 1 as follows:one nitrogen atom (N₁) is bound to one carbon atom (R₁═C₂H₅O) and 3hydrogen atoms (R₂, R₃ and H), and there is one chloride counteranion(X₁═Cl—). The removal process can be performed at any temperaturesuitable to support solvation of the alkaline earth salt formed byreaction with the organic amine cation/counterion pair. In someembodiments of the inventive concept the removal can be performed in atemperature range of about 0° C. to about 120° C. In other embodimentsof the inventive concept the removal can be performed within atemperature range of about 20° C. to about 100° C. In a preferredembodiment of the inventive concept the removal can be performed withina temperature range of about 20° C. and about 70° C., advantageouslyreducing the need for temperature control equipment.

As shown in step C of FIG. 1 the lixiviant can enter or mix with theslag and, as shown in step D of FIG. 1, effectively remove an alkalineearth hydroxide, for example calcium hydroxide (Ca(OH)₂), by theformation of a soluble alkaline earth cation/counterion pair 150 (inthis instance, calcium chloride (Ca(Cl)₂)). The reaction can be stirredduring the removal process in order to improve reaction kinetics. Insome embodiments stirrer speeds can range from about 100 rpm to about2000 rpm; in other embodiments of the inventive concept stirrer speedscan range from about 200 rpm to about 500 rpm. Equation 6 depicts acritical chemical reaction in such a removal (in this case calcium, fromsteel slag that contains contaminants). Note that MEA.HCl dissociates inwater into monoethanolammonium cation (HOC₂H₄NH₃+(MEAH+)) and chlorideanion (Cl—). Reaction products include soluble CaCl₂ and unchargedmonoethanolamine (MEA)).

Ca(OH)₂(s)+2HOC₂H₄NH₃+(aq)+2Cl-(aq)→CaCl₂(aq)+2HOC₂H₄NH₂(aq)+2H₂O(l)  Equation 6

The removal process can be performed for any suitable length of time, asdefined by the amount and quality of the material to be processed andthe degree of carbonate forming metallic element removal desired. Insome embodiments of the inventive concept the removal can be performedfor 0.5 hours to 24 hours. In other embodiments the removal can beperformed for about 30 minutes. In preferred embodiments of theinventive concept the removal can be performed for about 15 minutes.Depending in part on the organic amine species used in the lixiviant,the pH of the solution can change during the removal process, forexample increasing as the alkaline earth element is removed from theslag. In some embodiments of the inventive concept the pH of thesolution at the beginning of the removal can range from about 6 to about13. In other embodiments of the inventive concept the pH at the end ofthe removal step can range from about 10 to about 12.

Removal of a carbonate forming metallic element with a lixiviant leavesinsoluble processed slag which has improved mechanical properties, owingto the lack of metals that form relatively mechanically unstablecarbonate salts upon environmental exposure. This can be recovered by avariety of means, including settling, centrifugation, and filtration, asin 165 of step D in FIG. 1. In preferred embodiments of the inventiveconcept insoluble processed slag is removed by filtration, for examplein a filter press that produces a filter cake. In order enhance theefficiency of the process, a filter cake from such a filtration can bewashed to remove additional calcium. In some embodiments the filter cakecan be treated with a wash volume that is about 10 times that of thewetness of the filter cake. In preferred embodiments of the inventiveprocess lower volumes can be used, for example about 5 times that of thewetness of the filter cake or about 3 times that of the wetness of thefilter cake.

Following separation of the soluble aqueous fraction or supernatant fromthe processed slag 165, the lixiviant can be regenerated and thesolubilized alkaline earth element removed from solution by the additionof a precipitant 170, for example carbon dioxide (CO₂), as shown insteps E and F of FIG. 1. The precipitant acts to form an insoluble saltwith the alkaline earth element (see step E of FIG. 1). Surprisingly,inventors have found that CO₂ precipitation of alkaline earth chlorides(for example, CaCl₂) can proceed efficiently at an acidic pH (i.e.,pH<7). Addition of CO₂ also generates the organic aminecation/counterion pair, as shown in step F of FIG. 1 and in Equation 7,thereby regenerating the lixiviant.

CaCl₂(aq)+2HOC₂H₄NH₂(aq)+2H₂O(1)+CO₂→CaCO₃(solid)+HOC₂H₄NH₃+(aq)+Cl—  Equation 7

In the exemplary reaction the precipitant forms calcium carbonate(CaCO₃) 180 which, being relatively insoluble, can be easily recoveredfor additional processing and, if desired, recovery of calcium. Forexample, CaCO₃ can be recovered using a filter press, as describedabove. The regenerated lixiviant can be recycled into the process 185,advantageously reducing the overall need for lixiviant and increasingprocess efficiency as more slag is processed.

The precipitation reaction can be performed at any temperature suitableto support the solubility of the precipitating agent (for example, CO₂)and maintain the insolubility of the precipitated salt. In someembodiments of the inventive concept the precipitation reaction can beperformed at about 4° C. to about 100° C. In other embodiments theprecipitation reaction can be performed at about 20° C. to about 80° C.In preferred embodiments of the inventive concept the precipitation canbe performed at about 40° C. to about 80° C. The concentration of CO₂gas supplied can range from about 0.1% to about 100%. In someembodiments of the inventive concept the concentration of CO₂ gas canrange from 10% to about 100%. This advantageously permits relatively lowquality sources of CO₂, for example flue gas or other waste gases, to beutilized. The CO₂-containing gas can be applied at any rate suitable forconversion of essentially all of the calcium present to CaCO₃ within asuitable time, for example about 3 hours to about 4 hours. Suitable flowrates can range from 1 L/hour/mol Ca to about 100 L/hr/mol Ca. Inpreferred embodiments of the inventive concept the flow rate for CO₂containing gas can be about 10 L/hour/mol Ca to about 20 L/hour/mol Ca.The pH of the solution can change during the precipitation reaction.

The pH of a working solution can change during the precipitation step.In some embodiments of the inventive concept, the starting pH of thesolution can range from about 9 to about 12, and can range from about 6to about 8 at the end of the precipitation. Advantageously, this pHshift can be monitored to provide an indication of the progress of aprecipitation reaction. Surprisingly, inventors have found that such aCO₂ precipitation of alkaline earth chlorides (for example, CaCl₂) inthis process can proceed efficiently at an acidic pH (i.e., pH<7). Theprecipitation reaction can be performed until a suitable endpoint isreached. For example, in some embodiments the precipitation can beperformed until the pH of the reaction remains below a specifiedsetpoint (for example, a pH of about 8) for at least about 15 minutes.

Separation of a precipitated alkaline earth (e.g. calcium and/ormagnesium) can be accomplished by any suitable method, includingremoving the soluble aqueous fraction from the tank 100 (for example, bydecanting, pumping, or siphoning), filtration, centrifugation, or acombination of these. In a preferred embodiment the precipitate isremoved using a filter press. The resulting filter cake can be easilyrecovered for additional processing and, if desired, recovery ofcalcium. The regenerated lixiviant can be recycled into the nextiteration of the process 185, advantageously reducing the overall needfor lixiviant and increasing process efficiency as more raw materialscontaining alkaline earths are processed.

It should be noted that the choice of lixiviant can allow for theselective removal of calcium in this example because it does not reactwith other metals (ME) or metal oxides/hydroxides (MEO_(x)) in the slag,as shown in Equation 8 and Equation 9.

ME(s)+HOC₂H₄NH₃+(aq)→NO REACTION   Equation 8

MEO_(x)(s)+HOC₂H₄NH₃+(aq)→NO REACTION   Equation 9

The soluble calcium salt and the soluble MEA from Equation 6 can easilybe separated from the processed slag. Once separated, the solubleaqueous fraction can utilized in other processes as-if, providing thetarget process can withstand the small quantity of lixiviant as acontaminant. Alternatively the soluble aqueous fraction can be furtheredprocessed as needed.

In an alternative embodiment of the inventive concept, a soluble aqueousfraction containing a solubilized alkaline earth cation/counterioncomplex as shown in Equation 6 can be concentrated or diluted to adesired strength as required by the end user. Alternatively, such asolution can be boiled down or evaporated completely, leaving analkaline earth element cation/counterion salt and/or various hydratesthereof, depending on how vigorously the mixture is dried. The residualuncharged organic amine could also be removed by this process andoptionally captured for reuse. The dried alkaline earth elementchlorides can be further processed into oxides via thermal oxidation,precipitation with agents such oxalic acid, sodium hydroxide, potassiumhydroxide or other precipitating agents.

There are of course many possible lixiviants of the form of Compound 1,and there are likewise many alkaline earth element sources. While theexamples provided have described the action of two organic aminelixiviants (i.e., ammonium chloride and monoethanolamine hydrochloride(a.k.a. monoethanolammonium chloride) with one particular source (steelslag) of a particular alkaline earth element (calcium) other examples ofprocess of the inventive concept can utilize organic aminecation/counterion pairs such as ammonium acetate, monoethanol-ammoniumacetate, ammonium nitrate, or monoethanolammonium nitrate.Alternatively, biologically derived lixiviants such as the amino acidglycine (or a salt of itself) or the hydrobromide salt of poly-L-lysinecan be used. Similarly, while examples note the use of steel slag, othersources (such as calcite, dolomite, gypsum, plagioclases, amphiboles,pyroxenes and garnets) are suitable. Alternatively, systems, methods,and compositions of the inventive concept can be utilized to recoveralkaline earth elements from agricultural waste, consumer waste,industrial waste, scrap or other excess materials from manufacturingprocesses, or other post-utilization sources.

Many alkaline earth elements can form hydroxides; most of these havevery limited solubility in water. These hydroxides also have varyingdegrees of basicity. While calcium hydroxide present in many industrialslags has been cited as an example there are many other alkaline earthelements that form suitable bases in water and can be problematic ifpresent in significant quantities in a processed slag. Examples of suchother elements include magnesium, beryllium, strontium, barium, andradium. Such salts have different basicities, which can be paired withorganic amine based lixiviants of different acidities to provideselective recovery.

It should also be noted that systems, methods, and compositions of theinventive concept are not limited to one alkaline earth species beingremoved with one particular lixiviant or set of anions. Multiplealkaline earth species with various organic amine based lixiviants andvarious anions (or acids) can be used in sequence or in parallel toremove a particular mixture of metals or to produce a processed slaghaving a particular composition.

As described above, lixiviants of the inventive concept can be appliedin a variety of methods. Examples of some of these methods are depictedschematically in FIG. 2, FIG. 3, and FIG. 4.

FIG. 2 depicts a method of the inventive process 200 in which a slag210, for example an iron/steel slag containing an alkaline earthelement, is mixed with a lixiviant 220. The lixiviant can include one ormore organic amine species as described above in the form of a cation,coupled with a suitable counterion. Suitable counterions can includehalides. In a preferred embodiment of the inventive concept thecounterion is chloride (Cl—).

A sample 210 can be a calcium-containing iron/steel slag or any suitableslag or other industrial waste that includes a carbonate-formingalkaline earth (e.g. calcium and/or magnesium). The slag 210 can betreated prior to mixing with the lixiviant 220. For example, thecomponents of the sample 210 can be reduced in size, for example throughmilling, grinding, pulverizing, or sifting. Such processes improve thesurface area to volume ratio of elements of the slag and can serve toincrease reaction rates and/or efficiency of removal of carbonateforming metals and salts. In some embodiments a slag can be chemicallytreated, for example through exposure to strong bases (such as sodiumhydroxide) or oxidized through exposure to air at elevated temperatures.Such chemical treatments can serve to generate alkaline earth metalsalts (for example, hydroxides or oxides) and to alter the physicalstructure of the slag or components of the slag.

On interacting with the lixiviant 220, alkaline earth elements in theslag interact with organic amine cations and counterions to form asoluble alkaline earth element cation/counterion complex that issolubilized in the aqueous supernatant 230, along with an unchargedorganic amine. The pH of this portion of the reaction process can bealkaline (i.e., ranging from about 7.5 to about 14). In some embodimentsof the inventive concept the pH can range from about 10 to about 12.Slag from which such alkaline earth elements have been extracted remainsbehind as insoluble material, for example as a processed slag 240 thatcan be utilized for various construction material and/or fill purposesor further processed if desired.

The processed slag 240 can be separated from the aqueous supernatant 250by a variety of processes, including settling, filtration, orcentrifugation, either alone or in combination. If desired, the alkalineearth cation 260 can be recovered from the aqueous supernatant 250 byany suitable means, including electrodeposition, precipitation, and ionexchange. In a preferred embodiment of the inventive concept thelixiviant species is regenerated by the addition of a precipitant (Pr)to produce an insoluble alkaline earth salt, which can be readilyrecovered if so desired. Such precipitants can be an H+ donating speciessuitable for forming insoluble salts of alkaline earth elements whileregenerating an organic amine cation, for example CO₂ or carbonic acid,chromic acid, or sulfuric acid. In a preferred embodiment of theinventive concept the precipitant (Pr) is CO₂ or carbonic acid.Surprisingly, inventors have found that this precipitation can beperformed at a pH of less than 7. In such an embodiment a precipitationstep can be performed at a pH between about 6 and about 7. In apreferred embodiment a precipitation step can be performed at a pH ofabout 6.7. As noted above, the uncharged organic amine remaining in thesupernatant 250 is regenerated 270 in this process to form an organicamine cation that can form part of a lixiviant 220 that can be used inthe next iteration of the reaction. This recycling of the lixiviantgreatly reduces consumption through multiple cycles of the process andadvantageously reduces environmental impact and expense.

Other embodiments of the inventive concept can advantageously utilizethe selective complex formation and solubility of components of methodsof the inventive concept to remove different alkaline earth elementsfrom the same slag. One example of such a method is shown in FIG. 3. Asshown, such a method can be a chain of reactions that are, essentially,one or more repetitions of the method shown in FIG. 1 applied to aprogressively depleted slag. In an example of such a method 300, a slag305 and a first lixiviant 310 are brought into contact with each other.The first lixiviant 310 includes a first organic amine cation and acounterion, and reaction 315 with the slag 305 produces a firstprocessed slag 320 and a first aqueous supernatant 325 that includes afirst alkaline earth cation, a counterion, and an uncharged organicamine. The first processed slag 320 includes materials that were notreactive with the first lixiviant, which can include additional alkalineearth elements, potentially valuable materials, and unwantedcontaminants. The first process slag 320 can be separated from the firstaqueous supernatant 325 by any suitable method, including settling,filtration, and centrifugation, either alone or in combination. Ifdesired, the first alkaline earth cation can be recovered from the firstsupernatant 325 by any suitable means, including electrodeposition,precipitation, and ion exchange. In a preferred embodiment of theinventive concept a first precipitant (Pr 1) can used that generates aninsoluble first alkaline earth salt and regenerates the first organicamine cation/counterion pair 330. In such an embodiment the unchargedfirst organic amine remaining in the aqueous supernatant 325 can, inturn, be regenerated 360 to give a first organic amine cation that canform part of a first lixiviant 310 that can be used in the nextiteration of the process.

The first processed slag 320 can, in turn, be contacted 340 with asecond lixiviant 335 that includes a second organic aminecation/counterion pair. Reaction with the first processed slag 240produces a second processed slag 350 and a second aqueous supernatant345 that includes a soluble second alkaline earth elementcation/counterion complex and uncharged second organic amine. If sodesired, the second alkaline earth cation can be recovered from thesecond aqueous supernatant 345 by any suitable means, includingprecipitation, electrodeposition, and/or ion exchange. In a preferredembodiment of the inventive concept a second precipitant (Pr2) can usedthat generates an insoluble second alkaline earth salt and regeneratesthe second organic amine cation/counterion pair 355.

Such precipitants can be an H+ donating species suitable for forminginsoluble salts of alkaline earth elements while regenerating an organicamine cation, for example CO₂ or carbonic acid, chromic acid, orsulfuric acid. The regenerated second organic amine/counterion pair canin turn be recycled 365 for use in the next iteration of the process. Insome embodiments of the inventive concept the first precipitant and thesecond precipitant are the same species. In other embodiments of theinventive concept the first precipitant and the second precipitant aredifferent species. In a preferred embodiment of the inventive conceptthe first precipitant and the second precipitant are CO₂ or carbonicacid. In some embodiments of the inventive concept the second processedslag 350 is subjected to further rounds of treatment with lixiviants inorder to remove additional carbonate-forming metallic elements. Thisrecycling of the lixiviants advantageously reduces the overall amount oforganic amines used as the process is repeated, which limits both theenvironmental impact of such operations and permits considerable savingsin materials.

Another embodiment of the inventive concept that permits removal of twoor more alkaline earth elements from a slag is shown in FIG. 4. In sucha method 400 a slag 410 is contacted with a lixiviant 420 that includesa first organic amine cation/counterion pair and a second organic aminecation/counterion pair. This mixture 430 results in a processed slag 450and a first aqueous supernatant 440. This first aqueous supernatant caninclude a first alkaline earth element cation/counterion pair, a secondalkaline earth element cation/counterion pair, a first uncharged organicamine, and a second uncharged organic amine. If desired, the firstalkaline earth cation 460 can be recovered from the first aqueoussupernatant 440 by any suitably selective means, includingprecipitation, electroplating, or ion exchange. In some embodiments ofthe inventive concept, the first alkaline earth element can be recoveredby adding a first precipitant (Pr1) that selectively forms an insolublesalt of the first alkaline earth element 460. For example, in a slagthat contains magnesium and calcium, the calcium can be removed andoptionally recovered in this step of the reaction by the addition ofchromic acid as a first precipitant (P1) to form relatively insolublecalcium chromate (CaCrO₄); relatively soluble magnesium chromate(MgCrO₄) would remain in a second aqueous supernatant 470.

Recovery of the second alkaline earth cation from the second supernatant470 also yields a regenerated lixiviant. If desired, the second alkalineearth cation can be recovered from the second supernatant 470 by anysuitable means, such as precipitation, electrodeposition, or ionexchange. In some embodiments the second alkaline earth element can berecovered by adding a second precipitant (Pr2) that forms an insolublesalt of the second alkaline earth element and completes regeneration ofthe lixiviant 480. For example, in a sample containing a mixture ofmagnesium and calcium, the magnesium can be recovered in this step ofthe reaction from a supernatant resulting from chromic acid treatment bythe addition of CO₂ or carbonic acid as a second precipitant (P2) toform relatively insoluble calcium carbonate (CaCO₃). The regeneratedlixiviant can in turn be recycled 490 in the next iteration of theprocess.

In some embodiments of the inventive concept the first organic amine andthe second organic amine (and their respective cations) can be differentmolecular species with different acidities and/or specificities foralkaline earth elements. In other embodiments of the inventive conceptthe first organic amine and the second organic amine can be the samemolecular species, with selectivity between the first alkaline earthelement and the second alkaline earth element being provided by themethod used for their recovery from supernatants. For example,utilization of different precipitating species, utilization of the sameprecipitating species under different conditions (for example,concentration, temperature, pH, or a combination of these), utilizationof ion exchange media with different selectivities, or combinations ofthese approaches can be used to provide selective recovery of thealkaline earth elements of a sample. It should be appreciated that, asdescribed in the processes illustrated in FIG. 2 and FIG. 3, thatregeneration and re-use of the lixiviant through repeated iterationsadvantageously reduces the amount of organic amine needed, which limitsboth the environmental impact of such operations and permitsconsiderable savings in materials.

Another embodiment of the inventive concept is a processed slag withreduced content of carbonate-forming metallic elements relative to aslag starting material. Such a processed slag can be produced byselective removal of carbonate-forming metallic elements (such ascalcium and/or magnesium) from a slag raw material by one or more of theprocesses described above. Such a processed slag has a reduced tendencyto form carbonates on exposure to air and moisture. Since formation ofsuch carbonates leads to expansion and fracturing of slag materials theprocessed slag exhibits improved mechanical and/or physical stability(e.g. increased resistance to lateral stress, increased resistance tocompressive stress, reduced degree of fragmentation over time, etc.)relative to the untreated slag raw material and is better suited for usein construction materials and/or in a load bearing capacity (e.g. in afill). In some processed slags removal of one or more carbonate-formingmetallic elements (e.g. calcium and/or magnesium) is nearly (i.e.greater than 90%) complete. In other processed slags the removal of oneor more carbonate-forming metallic elements is partial (i.e. greaterthan 10%, 20%, 30%, 40%, 50%, or more), but nevertheless sufficient toprovide improved mechanical and/or physical characteristics relative tothe corresponding untreated slag raw material.

Another embodiment of the inventive concept is a construction and/orpaving material produced using a slag material processed to remove atleast a portion of carbonate-forming metallic elements found in acorresponding untreated slag. Examples of such construction and/orpaving materials include concrete, concrete aggregate, concrete sand,cinder blocks, asphalt aggregates, road bed materials, railroad bedmaterials, and fills. Other embodiments of the inventive concept includefiltration materials and agricultural supplements (e.g. mineralsupplements) produced using a processed slag of the inventive conceptand having a reduced content of carbonate-forming metallic elementsrelative to a slag starting material.

A specific example of the removal of calcium from steel slag is shown inFIG. 5 and FIG. 6. FIG. 5 shows the composition of a typical steel slag,showing a complex mixture of various metal oxides including calciumoxide (CaO), which becomes calcium hydroxide (Ca(OH)₂) on exposure towater. Processing of such a steel slag is shown diagrammatically in FIG.6. Initially, steel slag (or an alternative calcium source) is ground600 to less than around 125 μm. This greatly increases the surface areaavailable for reaction. Water and lixiviant are mixed 610 in a suitableratio, which can range from 1% to about 50%. The ground slag and aqueouslixiviant are mixed 620 and stirred or agitated for a time sufficient toform the calcium cation/counterion pair, in this instance approximately10 minutes. The processed slag, which is depleted of calcium, is removedby filtration 630 and the liquid fraction or supernatant is processed byadding carbon dioxide (or an equivalent, such as carbonic acid) toprecipitate calcium carbonate (CaCO₃) 640. This process also regeneratesthe lixiviant. The CaCO₃ can then be prepared for further processing bywashing, dilution into a slurry, and so on 660, while the regeneratedlixiviant is recycled for re-use in the next iteration of the process670.

Examples of the recovery of calcium by systems, methods, andcompositions of the inventive concept are shown in FIG. 7A through FIG.7D. FIG. 7A shows the change in pH over time as calcium is removed fromlow-grade lime using monoethanolamine-HCl (MEACL) as the organic aminelixiviant. In this reaction 5 grams of low-grade lime was mixed with 50grams of water containing the lixiviant at a lixiviant to calcium molarratio of 2.1:1, while stirring 400 rpm. The reaction was allowed toproceed for 23 minutes. FIG. 7B shows the results of a similar study, inwhich the pH was monitored over time as calcium is removed fromlow-grade lime using glycine as the organic amine lixiviant. It shouldbe appreciated that as an amino acid glycine can be advantageouslyderived from biological sources and that, due to its zwitterionicnature, glycine can act as its own counterion. In this reaction 5 gramsof low-grade lime was mixed with 50 grams of water containing thelixiviant at a lixiviant to calcium molar ratio of 2.1:1, while stirringat 400 rpm. The reaction time was allowed to proceed for 24 minutes.FIG. 7C shows the results of recovery of removed calcium using aprecipitant, in this instance CO₂. In this example pH was monitored asCO₂ was perfused through calcium removed from low grade lime usingmonoethanolamine-HCl as the lixiviant. The reaction was performed for 11minutes as 100% CO₂ was perfused through the solution at 20 mL perminute at a temperature of 22° C., while stirring at 400 rpm.

It should be apparent to those skilled in the art that many moremodifications besides those already described are possible withoutdeparting from the inventive concepts herein. The inventive subjectmatter, therefore, is not to be restricted except in the spirit of theappended claims. Moreover, in interpreting both the specification andthe claims, all terms should be interpreted in the broadest possiblemanner consistent with the context. In particular, the terms “comprises”and “comprising” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps may be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced. Where the specification claims refers to at leastone of something selected from the group consisting of A, B, C . . . andN, the text should be interpreted as requiring only one element from thegroup, not A plus N, or B plus N, etc.

What is claimed is:
 1. A processed slag, wherein the processed slag isproduced by selective removal of an alkaline earth element from a slag,and wherein the processed slag comprises less than 60% of the alkalineearth element content of the slag.
 2. The processed slag of claim 1,wherein the processed slag comprises less than 40% of the alkaline earthelement content of the slag.
 3. The processed slag of claim 1, whereinthe processed slag comprises less than 20% of the alkaline earth elementcontent of the slag.
 4. The processed slag of claim 1, wherein theprocessed slag is characterized by having a reduced carbonate contentfollowing an environmental exposure relative to that of the slagfollowing the environmental exposure.
 5. The processed slag of claim 1,wherein the processed slag, following an environmental exposure, ischaracterized by having improved resistance to compressive stress orlateral stress relative to that of the slag following the environmentalexposure.
 6. A construction material comprising a processed slag,wherein the processed slag is produced by selective removal of analkaline earth element from a slag, and wherein the processed slagcomprises less than 60% of the alkaline earth element content of theslag.
 7. The construction material of claim 6, wherein the constructionmaterial is selected from the group consisting of concrete, concretesand, concrete aggregate, and asphalt aggregate.
 8. The constructionmaterial of claim 6, wherein the construction material is selected fromthe group consisting of road bed material, railroad track bed material,and fill material.